This invention relates to fault detection in electronic circuits and in particular to augmenting an electronic circuit with a fault detection system that can automatically and continuously test the circuit The reliance placed on electronic devices coupled with the increasing complexity of such devices establishes a need for an efficient and reliable means for determining whether there is a fault in an electronic circuit. Electronic circuitry that is used for navigation or weapons systems must have a high degree of reliability. An example of such a system is the Firefinder Doppler Filter circuit from the U.S. Army's AN/TPQ-36 radar signal processor subsystem. It is a concern with such systems that all faults are detected so that the circuit can be replaced or repaired. In such usages, it is also important to detect any intermittent faults because of the high degree of reliability demanded. Accordingly, it is very useful to be able to perform inspections on a regular, even continuous basis and to implement inspection into a technique that the circuit can perform automatically or under the control of a central computer that monitors and initiates self-inspection techniques for many circuits in a system or in several systems.
A methodology for accomplishing this type of fault detection is known as microdiagnostics. Microdiagnostics is a guided probe, troubleshooting technique based on software signature analysis, and is fully described by G. C. Bergeson in Microdiagnostics for Prototype Instrumentation, EGG-EA-7091, November 1985. The microdiagnostics approach relies on a human operator to correctly position a test probe at a given node of the printed circuit board under test. Since the fault diagnosis depends on the human operator, it is susceptible to human error and is slowed by human response time. In addition, microdiagnostics utilizes a software generated stimulus which usually operates at a slower rate than the normal system clock. These limitations can severely limit the reliability and utility of the microdiagnostics methodology.
Another concern with fault detection techniques is to apply it to existing equipment. Design of new circuits can account for self-diagnosis using current techniques. However, the need for self-implementing fault detection also applies to existing equipment that would be expensive and inefficient to replace. Although retrofitting is never as efficient as implementing a technique as part of the design process, the ability to retrofit a self-implementing fault detection technique can be very cost-effective for existing equipment which may have a history of repeated failure, but which cannot be immediately replaced.
Therefore, it is an object of the present invention to automate the microdiagnostics guided probe technique using a high-speed, hardware-based approach.
It is a further object of this invention to provide a built in device that is capable of applying a stimulus to a printed circuit board under test, analyzing the resulting circuit response, and isolating the associated fault if the response is abnormal.
It is a still further object of this invention to isolate a detected fault to a single integrated circuit package or small group of integrated circuits on a printed circuit board.
It is another object of this invention to totally automate the procedure of applying a test stimulus and interpreting the test data in a microdiagnostics methodology.
It is a still further object of this invention to provide a built-in circuit fault detection device that uses no external test equipment, requires no human interaction, and operates at the normal circuit speed in order to detect hard faults, dynamic faults, and timing faults.
It is a still another object of this invention to provide a circuit fault device that is capable of interfacing to a system level test controller, that can respond to test commands issued by the system test controller and that can communicate fault locations back to the controller where operational decisions can be made based on the discovered faults.
Still another object of this invention is to provide a circuit fault detection system that can diagnose itself for faults.
A still further object of this invention is to provide a circuit fault detection system that can be retrofitted to existing equipment.
It is another object of this invention to empirically determine the degree of fault coverage attained in the fault detection system.
It is another object of this invention to provide a fault detection system that is relatively simple and efficient so that it can be easily implemented into existing equipment at reasonable cost.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.